Scientists have discovered that the earthquake swarm around Santorini was caused by magma rising from great depths – recorded using advanced artificial intelligence and seabed sensors
The analysis of the earthquake swarm around Santorini reveals the origin of the “seismicity crisis” and its development.
In early 2025, the Greek island of Santorini and its surroundings experienced tens of thousands of earthquakes. A new study published in Nature by the Helmholtz Centre for Geospheric Sciences (GFZ) and GEOMAR in collaboration with international partners now provides the first detailed geological explanation for this event.
The study combined data from land-based seismic stations with measurements from instruments on the seabed near the underwater volcano Colombo (about 7 km from Santorini). The researchers used an advanced processing method supported by artificial intelligence to precisely find the epicenters of the tremors. The analysis shows that about 300 million cubic meters of magma rose from the depths of the crust and was stopped at a depth of about 4 km below the seabed. As it rose, the magma fractured the rocks around it and created thousands of tremors and microtremors.
Seismically sensitive area – the geological background
Santorini lies in the eastern Mediterranean Sea within the Hellenic Volcanic Arc – one of the most geologically active environments in the region. The islands of Santorini shape the rim of a caldera, formed by a massive eruption some 3,600 years ago – a seminal event in volcanic history.
Nearby is the active submarine volcano Colombo. The entire area is marked by several active fault systems, the product of the African plate pushing northeast against the Hellenic plate. The Earth's crust beneath the Mediterranean Sea is broken up into microplates that slide past each other, and in some cases even molten subplates - a source of continuous volcanic activity.
Santorini has recorded many eruptions in history, the last in 1950. In 1956, two strong earthquakes occurred in the southern Aegean Sea, just 13 minutes apart, between Santorini and the neighboring island of Amorgos, with magnitudes of 7.4 and 7.2 – and were accompanied by a tsunami.
The earthquake swarm that began in late January 2025 occurred precisely in this area. During the event, more than 28 earthquakes were recorded; the strongest of which exceeded magnitude 5.0. The intensity of the tremors caused great public concern, especially since it was initially unclear whether the cause was tectonic or volcanic in origin.
What happened below the sea surface? — Research findings
The new study shows that the earthquake swarm was triggered by magma flowing from deep below. The chain of events began as early as July 2024, when magma entered a shallow reservoir beneath Santorini—which initially led to a slight increase in the island’s elevation by a few centimeters. In early January 2025, seismic activity intensified, and by the end of January, magma began to rise from deep below—accompanied by intense seismicity.
However, the epicenter of the activity moved northeastward more than 10 km from Santorini. During this phase, the epicenters moved in several "pulses" from a depth of 18 km to a depth of only 3 km below the seabed. Combining high-resolution spatial and temporal analysis of the seismic dispersion with satellite interferometry (InSAR), terrestrial GPS stations, and seabed measurements allowed the sequence to be modeled.
Dr. Marius Isken (GFZ), geophysicist and lead co-researcher: “The seismicity pattern is typical of magma rising through the crust. The migrating magma breaks rocks and opens pathways for it — which generates intense seismic activity. Our analysis made it possible to accurately reconstruct the trajectory and dynamics of the magma rise.”
Following the movement of magma, renewed subsidence of Santorini was recorded—evidence, according to the authors, of the existence of an unknown hydrological link between the two volcanoes.
Dr. Jens Carstens (GEOMAR), lead co-investigator: “Thanks to close international cooperation and the combination of various geophysical methods, we were able to monitor the development of the event in almost real time – and even learn about the interaction between the two volcanoes. This will help improve future monitoring of both.”
Methods for mapping from many angles
Two factors enabled exceptional mapping of the subsurface:
- An artificial intelligence-driven method developed at GFZ for processing large seismic datasets.
- GEOMAR deployed underwater sensors in the Colombo Throat as part of the MULTI-MAREX project in early January. These sensors measured not only seismic signals above the reservoir, but also pressure changes resulting from the seafloor subsidence of up to 30 cm during the intrusion of magma beneath Colombo.
Scientific activity on Santorini continues despite the decline in seismicity. GFZ is conducting repeated measurements of gases and temperatures on the island, while GEOMAR currently has eight seabed sensing platforms operating.
Prof. Heidron Kopp (GEOMAR), marine geodesy researcher and director of MULTI-MAREX: "We have shared the findings on an ongoing basis with the Greek authorities to enable a rapid and accurate assessment of the situation in the event of new earthquakes."
Co-researcher, Prof. Praskevi Nomiko (University of Athens), adds: “The long-standing partnership enabled joint management of the events at the beginning of the year and their in-depth scientific analysis. A precise understanding of the dynamics in such an active region is critical for public safety.”
Volcanic crisis reveals coupled magma system at Santorini and Columbus,Nature, 24 September 2025. DOI: 10.1038/s41586-025-09525-7.
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